While not limited thereto, the present invention is particularly adapted for use in an airborne rendezvous and closure of two aircraft for the purpose of aerial refueling. Such refueling procedures are hazardous without good visibility conditions using present techniques. Normal aircraft radars have insufficient resolution at close range to permit closing to less than 500 feet. As a result, human visibility is needed for the last few hundred feet which are the most critical. The entire operation depends upon the skill of the receiver-aircraft pilot and boom operator without any other aids other than radio communication until a hook-up has been achieved, at which time boom sensors provide position data.
Laser systems, such as that shown in U.S. Pat. No. 3,917,196, have been provided for aircraft rendezvous and closure wherein a modulated light beam from one aircraft is reflected from another aircraft by a retroreflector. Azimuth and elevation positions are obtained by focusing the reflected light beam onto the face of an image disector tube; while range is determined by comparing the phases of the transmitted and received light beam modulation. Such laser systems are extremely accurate; however they cannot be used under certain cloud conditions and have a range no greater than about 500 feet under high background lighting conditions. As a result, other means must be provided for guiding a trailing aircraft beyond that range and under cloudy conditions.